The other ultrasonic with the conventional buzzer (20mm diametre, less than
1mm thick) claims 30W!!!
Now, I understand the difference with a "real" ultrasonic with two "real"
transducers I have had. Time comparison for the same cleaning results:
a. Real ultrasonic 60W : 0.5 min
b. the ultrasonic we talk (50W) : 9 min
c. the other ultrasonic with the buzzer (30W) : > 25 min...
Look at it another way. Why would you need a 7 amp relay to supply
power to a "buzzer"? Why would you need such a large heatsink and two
high current (?) transistors?
I suggest you buy something like this ...
http://www.p3international.com/products/special/P4400/P4400-CE.html
.... and measure the power consumption for yourself.
Yes, I thouhgt the second overtone.
I don't know to say if it's correct or not. I'm just thinking.
1.. The transducer (ceramic ultrasonic transduder, like a bigger buzzer) it
has a mass of say 25g. It is glued on the tank, say 100g. And the tank is
filled with water 400-600g. I wonder for its resonance frequency.
2.. Just a question because I don't know. Could someone take a conventional
small buzzer and make a circuit to work on the buzzer's resonace frequency,
relying on the buzzer's characteristics without RC or other similar parts on
the oscilator? If yes, then it is a possibility to be the same in this
machine.
I had another look at the following patent. It suggests that a simple
change to your circuit may enable your transducer to resonate at the
first overtone (see Fig 3 of the PDF file). It also confirms that the
resonant frequency is dependent on the mass of water.
OSCILLATOR CIRCUIT FOR AN ULTRASONIC CLEANER
http://www.freepatentsonline.com/3584244.html
The author states that "since the piezoelectric disc is closely
coupled to the tank and the water load, the water depth in the tank
effects the power transferred to the water and the resonant frequency
of the transducer".
"On all ultrasonic cleaning systems, some means must be employed to
control the frequency at which the generator drives the transducer. If
the generator is made to operate at a fixed frequency, poor
performance will be encountered, since it is generally not possible to
select one frequency which will always provide optimum operating
conditions."
"In the case of an ultrasonic generator, one is concerned with the
behaviour of a piezoelectric transducer at the fundamental and perhaps
the lower order overtone frequencies."
This part looks very interesting:
====================================================================
The preference the circuit shows in operating in the vicinity of some
initially selected frequency is also desirable in suppressing
tendencies to run at overtone frequencies. In some circumstances,
however, this effect might not be great enough to completely prevent
operation at the overtone. For instance, if the series resonant
impedance of the fundamental frequency is slightly greater than at the
first overtone, the circuit preference for lower impedance could take
precedence and result in operation at the overtone were the shunt
capacitor 86 not employed.
Since the capacitor 86 is connected across the feedback transformer
primary, its capacitive reactance lowers the impedance to overtone
frequencies. This results in a lower primary voltage or, more
directly, an increase in core saturation time. Thus, any tendencies to
run an overtone are adequately suppressed, forcing the circuit to run
at the fundamental.
In the example given, it is desirable to operate at the fundamental
frequency. Nevertheless, if operation at an overtone is desired, this
may be accomplished by suitable selection of circuit elements and
constants, and the principles of the invention may be employed to
enhance operation at the preferred overtone.
====================================================================
- Franc Zabkar
